EFFECTS OF TEMPERATURE ON GROWTH OF METARHIZIUM FLAVOVIRIDE AND VIRULENCE TO THE VARIEGATED GRASSHOPPER, ZONOCERUS-VARIEGATUS

The temperature optima for germination, radial hyphal extension rate a nd sporulation were determined for two isolates of Metarhizium flavovi ride from acridoid hosts. 191-609 exhibited lower temperature optima f or hyphal extension (25.5 degrees C) and sporulation (24 degrees) than IMI 330189 (27 degrees and 25 degrees, respectively), although temper ature optima for germination were similar (ca 30 degrees). The tempera ture optimum for sporulation was lower than that for hyphal extension. Further studies were carried out on 191-609 to investigate the effect of temperature and dose on the infection mortality rate of the grassh opper pest, Zonocerus variegalus. Increasing dose resulted in a decrea se in mean survival time regardless of incubation temperature. Dose an d temperature were shown to interact, with the effects of dose increas ing at temperatures either side of the optimum. Furthermore, for each dose, the optimum temperature for infection was estimated to be ca 5 d egrees higher than the optimum for growth, and no significant relation ship was identified between hyphal extension rate in vitro and host su rvival time. The implications of these results are discussed with rega rd to the selection of isolates for use in biological control.